The piles of cheap clothing on our high streets come with a high price tag. We know about the low pay and poor working conditions of those producing these garments, as described in the work of writers such as Naomi Klein. What we know much less about is the impact of those working conditions on the workers' families. The next time you pick up an elaborately stitched jacket or pair of shoes, ask yourself where the seamstress's children were when she was hunched over her sewing machine.

A book to be published next month is a stab at tracking the impact of rapid economic globalisation on family life. Jody Heymann's Forgotten Families is based on research on hundreds of families in countries across the world, from Botswana to Vietnam and Mexico, and it quickly punctures some pervasive myths about extended families. Increasing numbers of women are taking up paid employment across the developing world and, at the same time, the migration from rural areas to cities is accelerating. The combination of these two is rupturing centuries-old traditions of child rearing and care - in particular, the habit of a mother keeping children with her while she worked in the fields or in the home, and the support offered by the extended family to help care for children.

A young mother working in a free-trade zone in Asia or central America rarely has her mother nearby to help out, and she can't take her child to a factory. The problems she faces are deeply familiar to women in the developed world - finding reliable childcare, coping when the child is sick or has school holidays - but the picture of how she copes (and the burden of coping does fall disproportionately on women) is dramatically more stark, according to Heymann's Harvard research project. Places at workplace nurseries are often limited or nonexistent, and employment rights, such as decent maternity leave or leave for a family emergency, are restricted. Heymann found that of the families they interviewed, 36% admitted they had had to leave young children at home alone, 39% had left a sick child at home alone and 27% had left a child in the care of another child.

Parents described in interviews with researchers how they had no choice but to leave eight-year-olds in charge of their toddler siblings, sometimes locking them into the home to try to ensure their safety. But safety is one of the biggest problems - in half of the families interviewed in Botswana and Mexico, children had suffered accidents while their parents were at work. Some were the result of children trying to cook meals for themselves and their siblings. Mothers recounted the anguish of leaving sick children because if they missed work their pay was docked - and they needed every penny to pay for the medicines required.

What makes the picture all the more bleak is that there is a bigger care burden in many developing countries, which makes the conflict between the demands of poorly regulated workplaces and care responsibilities acute. The ratio of children and elderly to working-aged adults is more than 50% higher than in the developed world and the illness rates are higher; Aids will hugely aggravate the care burden in countries across the developing world.

Burgeoning free-trade zones across Asia may well be improving the material conditions of many millions of families, but there is an uncounted cost in unmet needs in the care economy - the routine tasks of having and raising children, and caring for the sick and the elderly.

Work-life balance is not just part of the politics of the affluent west; it's part of a global story of how the organisation of economic life is invading ever more aggressively the processes and relationships of care. Increasingly, in the affluent west and the developing world, the inflexible demands of long hours of paid employment are prioritised over domestic responsibilities - leaving a care gap.

The solution in the west is to outsource care - pay someone else to do it - and that is often provided by migrant female labour from the developing world. So the care gap of the west is resolved at the cost of exacerbating the care gap of the developing world. It's bad enough when a woman has to leave her children alone to go to work in a factory for 12 hours a day; it's even worse when she has to get on a plane and leave her children behind for years at a time, using some of her pay to cover the cost of a maid substitute.

It's a form of asset-stripping - though this time the asset is not oil or diamonds but care. Alongside economic inequality emerges the inequality of care. It's what the American academic Arlie Russell Hochschild describes as the "care drain", as young women move to richer countries to care for the young, sick and elderly. The scale of this care drain is projected to grow dramatically; by 2020 the US alone will be able to absorb the entire world's supply of nurses, a demand in part generated by an increasingly elderly population.

For the first time in history, half of all migrants are women. In some countries, such as the Philippines, Sri Lanka and Thailand, women make up the majority of all migration. For many of them it is the need to earn to care for their own children that forces them to leave; the average age of migrant women entering the US is 29, an age by which most of them have had children.

To Hochschild, the family and the traditional caring roles of women represent the last "commodity frontier", as she explained in a lecture for the Young Foundation in London last month. In the 20th century the model of home and the wife was idealised as "a haven in a heartless world"; this was the one area of life kept separate from the principles of competition and efficiency and the market disciplines of economic life. No longer. Hochschild cites agencies advertising in her home state of California, such as Rent-A-Mom, which can undertake any domestic task from childcare to clearing out closets, sorting family photo albums, organising birthday parties and spending "quality time" with elderly relatives. All for a fee.

Hochschild insists that she is not describing some wacky Californian fad but the way in which affluent family life will evolve in the developed world. Already characteristics of this are evident, she would argue, in how we specialise ourselves and our emotional lives to fit the workplace - and pay others to provide the emotional skills needed in the home. She quotes the director of a San Francisco nursery that employs central American staff because they "know how to love a child better than middle-class white parents. They are more relaxed, patient and joyful ... these professional parents are pressured for time and anxious to develop their kids' talents." A mother who is a lawyer concurs with the analysis, conceding that her son's nanny is better for him than "anxious, busy parents like us".

Put the work of these two American academics alongside each other and you see how the nightmare worlds they describe interconnect in what Hochschild describes as "emotional imperialism"; a work-orientated west deskills itself of the emotional skills required for care - patience in particular - and imports them.